The invention relates to a press for hot isostatic pressing. The press is provided with means for rapidly cooling treated articles after pressing by removing pressurised gas from the furnace chamber.
Presses for hot isostatic pressing are known for a variety of end uses including compaction of articles made from powders, consolidation of castings and for gas bonding of articles. Such a Hot Isostatic Press (HIP) press usually operates within a wide rgange of temperatures and pressures, between 400 and 2000xc2x0 C. and between 300 and 2000 bar. A pressure medium such as argon gas is commonly used, but other fluids including liquids may also be used.
A HIP substantially consists of a pressure vessel in which a furnace is arranged. Such a furnace is usually adapted to be heated by means of electric heating elements arranged around the exterior walls of the furnace. Heating elements may alternatively be mounted in the bottom of the furnace. The electric heating elements are usually surrounded by a heat insulating mantle. The top and bottom of the furnace are each furnished with a heat insulating layer, forming a furnace chamber with heat insulated walls. Between the heat insulated furnace chamber and the pressure vessel wall is a space containing pressure medium. The pressure medium in the space surrounding the furnace chamber is usually cooler than the temperature of the pressure medium in the furnace chamber as the walls of the pressure vessel are generally cooled by the surroundings, if not by a cooling system arranged for that purpose.
For many applications it is desirable to cool the furnace chamber rapidly in order to obtain certain material properties. It is also generally desirable to remove treated articles as quickly as possible to obtain short production cycle times. In consequence it is also difficult to cool articles down to a temperature at which they may be conveniently handled and still achieve a short production cycle time.
It is known from U.S. Pat. No. 4,217,087 to promote cooling in a furnace chamber of a HIP by circulating amounts of a cooler inert gas from a space surrounding the furnace chamber inside the furnace chamber. This method gives a reduced cooling time but includes the use of a valve with moving parts incorporated in the walls of the pressure vessel. It is difficult and expensive to construct and maintain valves with moving parts inside the pressure vessel of a HIP because of severe stress from high pressure combined with high temperature.
In U.S. Pat. No. 5,251,880 a cooling system for a HIP is disclosed that comprises openings in the walls between a furnace chamber and a surrounding pressure vessel and associated opening and closing mechanisms. Openings in the top of the furnace chamber are disclosed. The circulation of gas surrounding the furnace chamber into the furnace chamber is facilitated under cooling. This device also incorporates a valve with moving parts which, similar to U.S. Pat. No. 4,217,087, is difficult and expensive to construct and maintain because of severe stress from high pressure combined with high temperature.
It is known from U.S. Pat. No. 5,123,832 to cool the furnace chamber of a HIP rapidly by the circulation of a cooler pressure medium through a furnace chamber. In this device for and method of cooling articles, one or more pumps or fans are arranged in the bottom of the pressure vessel and at the bottom of the furnace chamber. Cooling time is reduced by circulating proportions of a cooler gas from spaces between the walls of the furnace chamber and the walls of the pressure vessel into the furnace chamber by means of the pumps or fans. However a shortcoming of this apparatus is that a cooling stage takes place first, followed by a decompression stage, contributing to a somewhat lengthy production cycle time. It is also rather lengthy to cool articles to a sufficiently low temperature such that they are relatively easy to handle manually.
It is an object of the invention to provide a hot isostatic press. It is another object of the invention to provide a method to cool the treated articles in a hot isostatic press rapidly. It is a another object of the invention to rapidly cool treated articles such that they may be removed from the invention at a temperature at which they can be conveniently handled. It is a still further object to achieve improved control over the cooling rate of treated articles.
These and other objects are realised by a hot isostatic press according to the invention. The present invention is an isostatic press for hot isostatic pressing of articles, having a pressure vessel in which a furnace chamber is arranged with a space between the furnace chamber and the walls of the pressure vessel. The furnace chamber has a heat-insulating mantle and heat-insulating top wall and bottom wall, and one or more passageways are arranged in the walls of the furnace chamber. The present invention is characterised in that at least one gas outlet is arranged in the interior of the furnace chamber connected to means arranged outside the pressure vessel for receiving gas. When rapidly cooling treated articles, gas is removed from the interior of the furnace chamber by a gas outlet means such as a pipe.
The advantage of the present invention is that treated articles may be cooled rapidly. This gives a technical benefit of greater control over material properties and an economic benefit of shorter production cycle times. A shorter cycle time is produced by carrying out two stages, the cooling of the treated articles and the decompression of the gas at the same time. A further advantage is that the present invention is more efficient. First, treated articles inside the furnace chamber are cooled by a flow of cooler gas flowing in from the space surrounding the furnace chamber into the furnace chamber. Secondly, the greater part of the adiabatic cooling effect due to decompression of the gas is absorbed in the furnace chamber, further cooling the treated articles. A still further advantage is that isostaticly treated articles cooled rapidly in one application of the invention are cooled to around 250xc2x0 C. such that the treated articles are conveniently handled using protective gloves. Rapidly cooling treated articles by removal of the gas from the interior of the furnace chamber also permits both the temperature in the furnace chamber to be measured more directly via the gas flow. The gas flow past the articles is also under more direct control than with conventional methods in which gas is circulated from and removed from spaces surrounding a furnace chamber that contain cooler gas. The invention also has the advantage that no moving parts, such as valves for example, are required in or close to the furnace chamber. This simplifies construction and reduces the cost of an isostatic press for HIP according to the invention which, together with the shorter cycle time, significantly reduces the cost of treating articles in a HIP process.